package se.jagvetintedu;

public class Problem14 {

//	The following iterative sequence is defined for the set of positive integers:
//
//		n  n/2 (n is even)
//		n  3n + 1 (n is odd)
//
//		Using the rule above and starting with 13, we generate the following sequence:
//
//		13  40  20  10  5  16  8  4  2  1
//		It can be seen that this sequence (starting at 13 and finishing at 1) contains 10 terms. Although it has not been proved yet (Collatz Problem), it is thought that all starting numbers finish at 1.
//
//		Which starting number, under one million, produces the longest chain?
//
//		NOTE: Once the chain starts the terms are allowed to go above one million.

	private class Collatz {
		private Long start;
		private Integer count;
		
		Collatz(Long start) {
			this.start = start;
			this.count = 1;
			
			generate(start);
		}
		
		public Integer getCount() {
			return count;
		}
		
		public Long getStart() {
			return start;
		}
		
		public void generate(Long n) {
			while (n != 1) {
				count++;
				if (n%2 == 0) {
					n = n/2;
				}
				else {
					n = 3*n+1;
				}
			}
		}
	}
	
	public Integer test() {
		Collatz coll = new Collatz(13L);
		return coll.getCount();
		
	}
	public Long solve() {
		Long start = 1L;
		Long saved = start;
		Integer max = 0;
		
		while (start < 1000000) {
			Collatz coll = new Collatz(start++);
			if (coll.getCount() > max) {
				max = coll.getCount();
				saved = coll.getStart();
			}
		}
		
		return saved;
	}
	
	public static void main(String args[])
	{
		System.out.println("Project Euler, problem 14");
		
		Problem14 solution = new Problem14();

		System.out.println("The starting number below 1000000 with the longest Collatz chain is: " + solution.solve());
	}
}
